U.S. patent application number 11/366082 was filed with the patent office on 2006-09-07 for endovascular aneurysm treatment device and delivery system.
Invention is credited to Richard Allen Hines.
Application Number | 20060200234 11/366082 |
Document ID | / |
Family ID | 36953855 |
Filed Date | 2006-09-07 |
United States Patent
Application |
20060200234 |
Kind Code |
A1 |
Hines; Richard Allen |
September 7, 2006 |
Endovascular aneurysm treatment device and delivery system
Abstract
The present invention is directed to an intravascular treatment
for intracranial aneurysms. The invention consists of a patch stent
and, also, a patch stent delivery system allowing one to rotate the
stent to align the patch with the neck of the aneurysm. A
self-expanding nitinol framework holds the patch in place, a
radiopaque agent allows the patch location to be visualized and a
pusher tube that is mechanically locked into the unexpanded stent
is used to push the stent out of the catheter with rotational and
longitudinal control necessary to align the patch with the
aneurysm. A self-expanding framework is used to support a patch at
the neck of the aneurysm. The patch is designed to reduce the blood
circulation in the aneurysm and the stagnant blood will clot or
thrombus. The thrombus will stop any current blood leakage into the
brain and will dramatically reduce the possibility of future leaks
or potentially deadly ruptures. Over time the thrombus will be
absorbed and the volume of the aneurysm will shrink reducing
pressure on surrounding tissue.
Inventors: |
Hines; Richard Allen;
(Stilwell, KS) |
Correspondence
Address: |
Frank B. Flink, Jr, Esq.;Griffin, Flink, and Watson, LLC
8347 Fontana
Prairie Village
KS
66207
US
|
Family ID: |
36953855 |
Appl. No.: |
11/366082 |
Filed: |
March 2, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60658068 |
Mar 3, 2005 |
|
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|
Current U.S.
Class: |
623/1.49 |
Current CPC
Class: |
A61F 2/90 20130101; A61F
2230/0095 20130101; A61F 2002/823 20130101; A61F 2/0063 20130101;
A61F 2230/0008 20130101; A61B 2017/12054 20130101; A61F 2/82
20130101; A61B 17/12118 20130101; A61B 17/12022 20130101 |
Class at
Publication: |
623/001.49 |
International
Class: |
A61F 2/06 20060101
A61F002/06 |
Claims
1. A vascular stent for treating blood vessel defects comprising: a
patch, configured to cover a neck of an aneurysm and a support
framework configured to anchor the stent in an artery.
2. The stent as claimed in claim 1 further comprising a radiopaque
agent applied to the stent.
3. The stent as claimed in claim 2 wherein said patch is a disc
shape, said patch is self-expanding, said patch having proximal and
distal ends, and wherein said framework consists of a first and
second loop, the first said loop flexibly attached to the proximal
end of said patch and the second said loop flexibly attached to the
distal end of said patch.
4. The stent as claimed in claim 2 wherein said patch is a material
selected from the group of metal, plastic, or a combination of
metal and plastic, and wherein said patch is self-expanding.
5. The stent as claimed in claim 3 wherein said patch disc shape is
elliptical in configuration, wherein the elliptical shape has major
and minor axis dimensions of less than or equal to ten and six
millimeters, respectively.
6. The stent as claimed in claim 2 wherein said patch is a material
selected from the group of nitinol, polytetrafluoroethylene,
silicone, and polyester.
7. The stent as claimed in claim 3 wherein said patch is formed of
a mesh material, which mesh material has an open area less than 70
percent.
8. The stent as claimed in claim 3 wherein said patch is formed of
a mesh material, which mesh material has an open area less than 50
percent.
9. The stent as claimed in claim 1 wherein said patch is comprised
of a first and second disk, said support framework comprised of
nitinol configured to have a first disc and second loop and a
center portion between said loops, and wherein said center portion
is sandwiched between said first and second disks.
10. The stent as claimed in claim 9 wherein said patch is a
material selected from the group of a continuous film, a porous
film, a woven fabric, or a fibrous mat.
11. The stent of claim 3 further comprising a stent delivery
system, said delivery system comprising a catheter and a pusher,
wherein said catheter is a flexible tube defining a proximal end, a
central opening, and a distal end and wherein, prior to deployment
of said stent, said stent is located within said central opening
defined by said catheter, and said pusher has fingers which fingers
releasably engage said stent thereby providing longitudinal and
rotational control of said stent and wherein said engagement
releases when said stent expands beyond the distal end of said
catheter.
12. The stent as claimed in claim 11 wherein said pusher is a
flexible tube extending through the central opening defined by said
catheter, said pusher defining a central opening, and further
comprising a guidewire extending through the central opening
defined by said pusher.
13. The stent of claim 3 further comprising a stent delivery
system, said delivery system comprising a catheter, a pusher, and a
guidewire wherein said catheter is a flexible tube defining a
proximal end, a central opening, and a distal end and wherein,
prior to deployment of said stent, said stent is located within
said central opening defined by said catheter, and wherein said
pusher is a flexible tube extending through the central opening
defined by said catheter, said pusher defining a central opening,
and wherein said guidewire extends through the central opening
defined by said pusher, and wherein said guidewire further
comprises a fork, which fork is configured to releasably engage
said stent and thereby pull said stent towards said distal end of
said catheter, which fork releases said stent when said guidewire
is moved towards the proximal end of said catheter.
14. A vascular stent for treating blood vessel defects comprising:
a patch and a framework, wherein said patch is sufficiently solid
to reduce circulation into an aneurysm and said patch is configured
to be conformed to a portion of a blood vessel, and wherein said
framework is flexibly attached to said patch and said framework is
configured to support said patch against a wall of the blood
vessel.
15. The stent as claimed in claim 14 further comprising: a
radiopaque agent applied to the stent.
16. The stent as claimed in claim 15 wherein said patch is a disc
shape which is generally elliptical in configuration, said patch
having proximal and distal ends; and wherein said framework
consists of a first and second loop, the first said loop flexibly
attached to the proximal end of said patch and the second said loop
attached to the distal end of said patch.
17. The stent as claimed in claim 16 wherein said stent consists
essentially of nitinol.
18. The stent of claim 14 further comprising a stent delivery
system, said delivery system comprising a catheter and a pusher,
wherein said catheter is a flexible tube defining a proximal end, a
central opening, and a distal end and wherein, prior to deployment
of said stent, said stent is located within said central opening
defined by said catheter, and said pusher releasably engages said
stent thereby providing longitudinal and rotational control of said
stent and wherein said engagement automatically releases when said
stent expands beyond the distal end of the catheter.
19. The stent of claim 14 further comprising a stent delivery
system, said delivery system comprising a catheter, a pusher, and a
guidewire wherein said catheter is a flexible tube defining a
proximal end, a central opening, and a distal end and wherein,
prior to deployment of said stent, said stent is located within
said central opening defined by said catheter, and wherein said
pusher is a flexible tube extending through the central opening
defined by said catheter, said pusher defining a central opening,
and wherein said guidewire extends through the central opening
defined by said pusher, and wherein said guidewire further
comprises a fork, which fork is configured to releasably engage
said stent and thereby pull said stent towards said distal end of
said catheter, which fork releases said stent when said guidewire
is moved towards the proximal end of said catheter.
20. The stent of claim 16 further comprising a stent delivery
system, said delivery system comprising a catheter and a pusher,
wherein said catheter is a flexible tube defining a proximal end, a
central opening, and a distal end and wherein, prior to deployment
of said stent, said stent is located within said central opening
defined by said catheter, and said pusher releasably engages said
stent thereby providing longitudinal and rotational control of said
stent and wherein said engagement automatically releases when said
stent expands beyond the distal end of the catheter.
21. The stent of claim 16 further comprising a stent delivery
system, said delivery system comprising a catheter, a pusher, and a
guidewire wherein said catheter is a flexible tube defining a
proximal end, a central opening, and a distal end and wherein,
prior to deployment of said stent, said stent is located within
said central opening defined by said catheter, and wherein said
pusher is a flexible tube extending through the central opening
defined by said catheter, said pusher defining a central opening,
and wherein said guidewire extends through the central opening
defined by said pusher, and wherein said guidewire further
comprises a fork, which fork is configured to releasably engage
said stent and thereby pull said stent towards said distal end of
said catheter, which fork releases said stent when said guidewire
is moved towards the proximal end of said catheter.
22. A vascular stent for treating blood vessel aneurysms
comprising: a patch, a support framework, and a radiopaque agent;
wherein said patch is disc-shaped and configured to fit across a
neck opening of an aneurysm, said patch disc diameter up to 4
millimeters larger than the aneurysm neck opening, said patch
having proximal and distal ends; and wherein said framework
consists of a first and second loop, the first said loop flexibly
attached to the proximal end of said patch and the second said loop
attached to the distal end of said patch, said loops configured to
fixedly engage blood vessel walls and hold said patch against the
aneurysm neck, and wherein said patch and frame consist essentially
of super-elastic material so as to be self-expanding.
23. The stent as claimed in claim 22 wherein said patch disc shape
is elliptical in configuration, wherein the elliptical shape has
major and minor axis dimensions of less than or equal to ten and
six millimeters, respectively.
24. The stent of claim 22 further comprising a stent delivery
system, said delivery system consisting of a catheter and a pusher,
wherein said catheter is a flexible tube defining a proximal end, a
central opening, and a distal end and wherein, prior to deployment
of said stent, said stent is located within said central opening
defined by said catheter, and said pusher releasably engages said
stent thereby providing longitudinal and rotational control of said
stent and wherein said engagement automatically releases when said
stent expands beyond the distal end of the catheter.
25. The stent of claim 22 further comprising a stent delivery
system, said delivery system comprising a catheter, a pusher, and a
guidewire wherein said catheter is a flexible tube defining a
proximal end, a central opening, and a distal end and wherein,
prior to deployment of said stent, said stent is located within
said central opening defined by said catheter, and wherein said
pusher is a flexible tube extending through the central opening
defined by said catheter, said pusher defining a central opening,
and wherein said guidewire extends through the central opening
defined by said pusher, and wherein said guidewire further
comprises a fork, which fork is configured to releasably engage
said stent and thereby pull said stent towards said distal end of
said catheter, which fork releases said stent when said guidewire
is moved towards the proximal end of said catheter.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority based upon provisional
application 60/658,068 filed Mar. 3, 2005.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable.
COPYRIGHT NOTICE
[0003] Portions of the disclosure, including the figures, contain
material which is subject to copyright protection. The copyright
owner has no objection to the facsimile reproduction by anyone of
the patent document or the patent disclosure, as it appears in the
Patent and Trademark Office patent file or records, but otherwise
reserves all rights whatsoever.
TECHNICAL FIELD
[0004] The present invention is directed to the field of medical
and veterinary endovascular treatments of aneurysms and, more
particularly, treatment of neurovascular aneurysms.
BACKGROUND OF THE INVENTION
[0005] Neurovascular aneurysms are currently treated by two
methods. The original treatment is an open surgical procedure
called clipping that removes the aneurysm from the circulatory
system by placing a clip at the base of the aneurysm. A newer, less
invasive, endovascular procedure called coiling entails packing the
aneurysm with flexible platinum coils that reduce blood circulation
in the aneurysm and, thereby, triggering a thrombus in the aneurysm
that may stop blood leakage and reduce the threat of the aneurysm
bursting. Self-expanding nitinol stents are sometimes used with
coiling. The stents form a lattice over the entrance to the
aneurysm from the blood vessel, called the neck of the aneurysm, to
help keep coils from prolapsing into the parent artery.
[0006] An aneurysm is formed when a weak spot in an artery
stretches so thin that it is in danger of bursting from the
pressure of the blood it contains. It forms a bulge or a ballooning
area that may leak or rupture. An aneurysm that ruptures in a brain
artery causes a stroke. Aneurysms that have wide openings at their
base are called "wide neck" aneurisms and are the most difficult to
treat. Wide neck aneurysms generally are defined as having a neck
>4 mm or a dome-to-neck ratio <2.
[0007] About 5 million people in the United States currently have a
brain aneurysm, and about 25 percent of these are "wide neck"
aneurysms. In the United States it is estimated that as many as 18
million people will develop a brain aneurysm during their lifetime.
Every year it is estimated that more than 30,000 people suffer from
ruptured brain aneurysms. Ten to 15 percent of these patients will
die before reaching the hospital. More than 50 percent will die
within the first 30 days after rupture. Of those who survive,
approximately half suffer some permanent neurological deficit.
[0008] An aneurysm may cause pain from pressure on surrounding
organs, but often aneurysms have no symptoms. Aneurysms may be
discovered during routine medical exams or diagnostic procedures
for other health problems, but most often people are unaware of a
problem until a rupture occurs. As relatively simple, viable
treatments for aneurysms are developed physicians will look for and
find more silent aneurysms and treat them before they cause
problems.
[0009] The potential benefits of aneurysm treatments by clipping or
coiling often do not outweigh the risks, especially for patients in
whom remaining life expectancy is less than 20 years (those over
age 60).
[0010] Neurosurgical clipping involves a craniotomy, an invasive,
open surgical procedure with high risk. During this procedure, the
arteries are exposed and one or more clips are applied across the
neck of the aneurysm to stop blood from flowing into the aneurysm.
The risk of a craniotomy is exacerbated in patients with a recent
brain injury as well as in elderly or medically complicated
patients. There is potential for further injury to the brain and
additional neurological defect.
[0011] Endovascular coiling is a less invasive, non-surgical
technique that involves inserting detachable platinum coils via a
catheter into the aneurysm. The goal of endovascular coiling is to
tightly pack coils inside the aneurysm to restrict blood flow
within the aneurysm, and thus form a thrombus. The formation of a
thrombus leaves little or no liquid in the aneurysm, eliminating
the potential for the aneurysm to expand, leak or burst. The use of
platinum allows the coils to be visible via X-ray. Although the
endovascular coiling process plays a role in the treatment of brain
aneurysms, the process has limitations. When platinum coils fill
the aneurysm, the aneurysm size will remain basically the same and,
therefore, it will continue to interfere with surrounding tissue.
The coiling procedure requires a long learning process due to its
technical difficulty. The process is effective in only a small
percentage of aneurysms, such as the small neck aneurysms where the
coils are more likely to stay in place. In other aneurysms, the
coils are likely to protrude into the parent vessel with risk of
clot formation and embolism.
[0012] Physicians have begun using stents or balloon-stent
combinations in combination with coiling to improve the
effectiveness of coiling. A balloon may sometimes be used to push
the coils into or pack them into the aneurysm. With stent-assisted
coiling, a stent is used to line the artery and form a screen to
hold the platinum coils inside the aneurysm.
[0013] For direct treatment of neurovascular aneurysms, today's
balloon-expandable or self-expanding stent designs are inadequate.
Substantial open spaces in the walls of self-expanding stents and
balloon-expandable stents do not sufficiently cover the aneurysm to
block blood flow to the aneurysm. For example, in the
stent-assisted coiling procedure, physicians currently use a thin
self-expanding stent developed by the Boston Scientific
Corporation. This product was approved for use by the FDA in 2002
for use with coils for the treatment of wide neck, intracranial,
saccular aneurysms arising from a parent vessel with a diameter of
.gtoreq.2 mm and .ltoreq.4.5 mm that are not amenable to treatment
with surgical clipping. The flexibility of this Boston Scientific
stent is derived from its very open design. It is intended to keep
the coils in place, but the surface has a significant amount of
open space and is not intended to block blood circulation across
the neck of the aneurysm.
[0014] A stent with a greater percent solid area would restrict
blood circulation into the aneurysm and trigger a thrombus in the
aneurysm more effectively. In that event, the liquid aneurysm would
solidify, eliminating the danger of rupture or leakage. If the
aneurysm is filled with the thrombus only and no coils, the
aneurysm sack will shrink as the thrombus is absorbed, reducing
pressure on the surrounding tissue.
[0015] Stents are generally designed as cylindrical shells
comprised of interconnected elements or struts. The pattern of
struts on the surface of the cylinder allows a stent to be crimped
to a small diameter for delivery and to expand radially from the
small delivery diameter to a larger placement diameter once
positioned within the lumen. The final placement diameter of an
expandable stent is generally between 2.5 and 4 times the delivery
diameter. As a result, the surface of the expanded stent has a
significant amount of open space. At the small delivery diameter,
the metal struts of the stents cover about 50 percent of the
surface area of the stent. At the expanded placement diameter, the
area covered by the struts is only about 12 to 20 percent of the
stent wall. Current research indicates that a dense stent will
reduce flow into the aneurysm. The open area of a typical stent,
then, is a limitation with respect to treatment of an aneurysm.
[0016] Several additional types of stents and methods for making
stents have been described previously. For example, the documents
U.S. Pat. Nos. 6,080,191, 6,007,573, and 6,669,719 discuss stents
using methods involving rolled flat sheets. U.S. Pat. No. 6,361,588
discusses a helical stent that expands into a relaxed helical shape
when released from a catheter. U.S. Pat. No. 6,689,159 discusses a
radially expandable stent with cylindrical elements and where
expansion occurs when the stress of compression is removed. U.S.
Pat No. 6,723,119 discusses a stent that is longitudinally
expandable before and after expansion. These stents are a
self-expanding type that expand into a cylindrical shape. A
bifurcated stent design is discussed in U.S. Pat. No. 6,706,062 and
U.S. Pat. No. 6,770,091 (the '062 and '091 patents) in which two
portions of the stent are balloon expanded with two balloon
catheters or separate pressures. Each branch of the stent is
expanded once with a balloon.
[0017] Additional methods for treating aneurysms have been
suggested. For example, the document U.S. Pat. No. 6,569,190
discusses a method for treating aneurysms that involves filling an
aneurysmal sac with a non-particulate agent or fluid that
solidifies in situ. This process leaves a permanent lump cast in
the volume of the aneurysm. The lump is an undesirable side effect
of solidification of the aneurysm volume.
[0018] U.S. Pat. No. 6,056,767, SYSTEM FOR THE TREATMENT OF A BODY
DUCT AND PROCESS FOR ITS MANUFACTURE, describes a stent and
delivery system that provide a stent that could be placed against
the neck of an aneurysm but no provision for selective coverage of
just the neck limits its usefulness to relative straight sections
of arteries with no perforator (side branch arteries) that would be
blocked by the stent.
[0019] The pleated stent assembly of U.S. patent application Ser.
No. 10/695,527 filed on Oct. 28, 2003(the '527 Application)
describes a stent for endovascular treatments that has advantages
over other methods of treating aneurysms, in that, among other
things, it provides a relatively solid area for closing off the
aneurismal sac. However, the pleated stent of '527 application,
since it is solid over the full stent cylinder, is limited in that
it can not be used for aneurysms near side branch or perforator
arteries that would also be occulted by the stent. The
micro-pleated stent assembly of U.S. patent application Ser. No
11/031,899 filed on Jan. 7, 2005 (the '899 Application) describes a
stent for endovascular treatments of aneurysms that may be
patterned with a patch to block the neck of the aneurysm and avoid
any near by perforators. The stents of both '527 and '899 are
balloon expandable and made from a ductile material. Being
constructed from a ductile material limits their use to inside 10
the skull where the stents will not be crushed by external forces.
The ductile material must also be thick enough to be sufficiently
rigid to withstand vasospasms that could also deform the ductile
stent that has no capability to spring back. The necessity for the
stents to be thick and the need to use a balloon for delivery thus
limits the use of the stents of both the '527 and the '899
applications.
[0020] Thus, a number of limitations exist in the existing
technology for treatment of aneurysms. The risk associated with
open surgery often outweighs the potential benefits. Coiling is
limited to narrow neck aneurysms and is a technically challenging
procedure requiring poking a guidewire and many, often over 20
coils into the sack of a fragile aneurysm. Coils can prolapse into
the parent artery causing a life-threatening thrombus to form.
Stents of the '527 and '899 applications are limited to
intracranial applications and have limited deliverability.
BRIEF SUMMARY OF THE INVENTION
[0021] The current invention consists of a self-expanding patch
stent and delivery system. The stent is delivered endovascularly,
to cover the neck of an aneurysm and start a healing process that
eliminates the dangers of the aneurysm. A self-expanding,
preferably nitinol, framework holds the patch in place, and a
radiopaque agent allows the patch location relative to the aneurysm
to be visualized with standard x-ray angiography. A pusher tube,
engaged with the stent, is used to push the stent out of a
microcatheter with the rotational and longitudinal control
necessary to align the patch with the aneurysm. The patch and
framework, being self-expanding, will, upon release from the
catheter, flex to expand to a shape dictated by the original
shaping of the material. Thus, the self-expansion property is a
feature of the elasticity of the material utilized for the patch
and framework.
[0022] The preferable components of the patch stent are (1) the
patch, which is a generally circular or elliptical disc shape and
slightly larger than the neck of the aneurysm, and (2) a
self-expanding framework to hold the patch in place over the neck
of an aneurysm. The patch stent preferably contains radiopaque
elements to visualize the patch location.
[0023] The preferred patch stent delivery system consists of a
catheter, through which the stent, guidewire and pusher tube pass.
The distal end of the pusher tube has radial, outward protruding
fingers that engage the collapsed stent in the catheter. When
engaged the pusher tube allows the individual placing the stent to
control the longitudinal rotational position of the stent relative
to the outer catheter tube. When properly oriented the stent is
pushed out while the tube is pulled back. As the stent/finger
engagement point moves beyond the end of the catheter, the stent
expands to anchor into the artery and disengage from the fingers.
The pusher tube, guidewire and catheter are then removed. Until the
fingers disengage, the stent can be pulled back into the catheter
and relocated if necessary.
[0024] The patch preferably is a mesh-structure which is
sufficiently solid to reduce circulation in the aneurysm and to
trigger a thrombus. The patch solid area will typically be greater
than 50 percent. The patch may be constructed from metal, plastic,
or combinations of the two. Open areas in the patch structure will
improve the patch's flexibility to facilitate deliverability of the
stent and small open areas will also facilitate endothelialization.
The patch also may be constructed from nitinol,
polytetrafluoroethylene, silicone, polyester or any other
biocompatible material. The patch may consist of one or two thin
disks bonded to a nitinol framework. The framework may be
sandwiched between two disks. The patch material may be a
continuous film, a porous film, a woven fabric, or a fibrous
mat.
[0025] To allow the stent to be visualized angiographically, the
patch location preferably will be indicated by materials with high
radiopacity. This preferably would be accomplished by (1) pattern
electroforming bands of gold or other highly radiopaque materials
around selected nitinol struts, (2) construction of the patch from
a thin layer or layers of a highly radiopaque materials, for
example, gold or platinum, (3) coating or incorporating a
dissolvable layer of radiopaque material, for example, iodine or
iodixanol, into the patch or (4) combination of these
techniques.
[0026] The self-expanding patch framework preferably is constructed
from superelastic material, such as nitinol. The framework may be
constructed from a tube or a flat sheet. If constructed from a
tube, the cylindrical photolithography process taught in U.S. Pat.
No. 6,274,294(the '294 patent), CYLINDRICAL PHOTOLITHOGRAPHY
EXPOSURE PROCESS AND APPARATUS by Hines may be used to pattern a
thin walled tube. The tube may be formed by conventional drawing
techniques or may be formed by thin film sputter deposition.
Sputtered thin film nitinol would require heat treatment to convert
the amorphous as-deposited material to a crystalline material with
the desired superelastic properties. The pattern of the support
rings may be chosen to be compatible with forming from a flat sheet
or a less restrictive cylindrical photolithography method may be
used. Conventional 2D photolithography or cylindrical
photolithography would be followed by electro-etching or chemical
machining to remove the unwanted material, forming the framework.
Laser machining or conventional machining could also be used to cut
the stent pattern.
[0027] The framework would ultimately take the form of a pattern on
the surface of a cylinder. If built by removing material from the
wall of a tube, this would be the natural outcome. If the framework
pattern is formed from sheet stock, the pattern must then be held
against the surface of a cylindrical mandrel while being
heat-treated to lock in the shape. Typical nitinol compositions
would be annealed at about 500 degrees C. to obtain good
superelastic properties and transform the patterned sheet material
into a pattern cylindrical stent framework.
[0028] The framework would be very light and open to minimize the
potential to block a perforator artery. Perforators are side branch
arteries that may be found in the vicinity of an aneurysm.
[0029] The framework may consist of a screen or lattice network or
ring to support the thin patch material and one or more springy
sinuous bands to anchor the patch stent to the parent artery. The
light open structure would also facilitate folding or pleating the
device to fit into a catheter for delivery. The self-expanding
nature of the stent would allow it to recover from vasospasms,
common with aneurysm treatments. The stents could also be placed in
arteries outside of the skeletal framework where it would be
subject to external forces that could temporarily deform the artery
and stent.
[0030] The patch location preferably should be visible
radiographically to guide the patch's placement. A conventional
guidewire would be used to guide the catheter to a location just
proximal to the aneurysm. The guidewire could be located in the
lumen of the pusher tube and either threaded through or alongside
the stent. Alternatively, the guidewire could be removed after the
microcatheter is in position and the stent and stent pusher could
be inserted in the proximal end of the microcatheter and advanced
to the aneurysm.
[0031] The pusher tube will have one or two radial protruding
fingers that just fit inside the microcatheter. The proximal end of
the folded or pleated stent structure will engage the fingers,
locking the fingers to the stent as long as the proximal end of the
stent is in the catheter. Locking the fingers to the stent allows
the stent to be rotated and pulled back into the catheter if
necessary. Locking provides rotational and longitudinal control of
the patch stent and, thus, allows the patch to be located over the
neck of the aneurysm. During patch placement, with the patch
partially extending beyond the catheter and partially expanded, the
angular position of the patch relative to the neck of the aneurysm
can be viewed radiographically and adjusted to align the patch.
When aligned, the catheter is pulled back while the pusher is
adjusted to hold the patch in place with respect to the aneurysm.
Only when the framework is free from the catheter, and thus free to
expand, do the fingers locking the stent disengage. Once the
fingers locking the stent are disengaged, the pusher may be used to
hold the stent relative to the aneurysm while the microcatheter is
pulled back to free the stent. The catheter and pusher may then be
removed leaving the stent in place with the support rings anchored
into the parent artery.
[0032] In another embodiment, the patch would be guided into place
by the guidewire, rather than using the fingers on the pusher. In
this embodiment, the guidewire engages the patch directly.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 shows 2-dimensional patch stent prior to being formed
on to the surface of a cylinder. FIG. 2 shows a cross-section of an
artery with a patch stent deployed at an aneurysm. FIG. 3A shows a
transverse cross-section of a strut of the superelastic framework
over-plated with a radiopaque material. FIG. 3B shows a
longitudinal cross-section of a strut of the superelastic framework
over-plated with a radiopaque material. FIG. 4 shows a
cross-section of an artery and aneurysm with stent and delivery
catheter.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
[0034] In the preferred embodiment the stent framework is made of
superelastic nitinol. The patch is a continuation to the framework
but with a high percent solid area. The location of the patch is
made visible by an electroplated gold layer placed over selected
sections of the framework.
[0035] The framework preferably would be patterned from a
2-dimentional sheet of nitinol with a thickness between 10 and 50
microns. The sheet may be formed on a copper substrate by
sputtering from an appropriately alloyed nitinol target
(approximately 50 weight percent Ti and 50 weight percent Ni). The
sheet of nitinol is patterned as shown in FIG. 1 to a pattern
consisting of two elliptical rings 10 on opposite ends of a central
patch 20 connected to a flexible area 30. The minor axis of the
elliptical rings is slightly larger than the diameter of the artery
50 that will receive the stent. Artery diameters will typically be
between 2 and 4 mm. The major axis of the elliptical rings will be
the square root of 2 times the artery diameter to provide a patch
support that will lay in the artery at an angle of about 45
degrees. The central patch is designed to be slightly larger (2 to
4 mm) than the neck of the aneurysm. This results in a patch which
is generally an elliptically-shaped disc with minor and major axes
of up to 6 and 10 mm, respectively. The patch solid area will be
between 30 and 100 percent solid with about 70 percent being
typical. Standard 2-dimentional photolithography defines the
pattern and electro-etching is used to remove the unwanted nitinol.
The copper substrate is then dissolved creating the framework shown
in FIG. 1.
[0036] The framework as shown in FIG. 1 is coated with liquid
resist. The resist may be sprayed on or dip coated. If dip coated,
the excess may be removed by spinning so that centrifugal force
slings off most of the resist leaving a thin coating. After a
soft-bake, the resist is imaged from both sides to define the area
on the nitinol struts for gold electroplating. As shown in FIG. 3A,
areas of the nitinol strut 60 are gold plated to form bands 64 with
the edge of the bands 68 defined by photoresist. The gold bands 64
are located in areas of the nitinol struts designed for minimum
bending so that the gold added for radiopacity does no
significantly reduce the elastic properties of the framework.
[0037] Preferably, the flat framework is forced to conform to the
surface of a cylindrical ceramic mandrel after threading the
mandrel through the elliptical rings 10. The rings are bent at the
flexing point 30 at an angle of about 45 degrees. An outer split
cylindrical mold is used to force the patch to the cylindrical
surface of the ceramic mandrel. The cylindrical mandrel has a
diameter slightly larger than the artery 50, where the stent will
be deployed. The nitinol/gold stent is then heat treated at about
500 degrees C. to set the memory of the superelastic nitinol
framework to the cylindrical shape.
[0038] FIG. 4 shows the distal end of the delivery catheter with
the stent practically deployed. To deploy the stent, the guidewire
100 would be advanced beyond the aneurysm. The guidewire 100 would
typically be a standard 0.012 inch wire. The pusher tube 90 and
stent 70 are threaded over the guidewire 100 and the patch 20 of
stent 70 is rolled around the pusher 90 and engaged with fingers
92. The elliptical rings 10 are elongated to fit into the catheter
tube 80. Catheter tube 80 keeps the stent 70 locked to the fingers
until the tube is pulled proximally and/or the pusher and stent are
advanced distally until the stent springs away from the fingers.
While the stent 70 and the pusher tube fingers 92 are engaged, the
rotation of the proximal end of the pusher will rotate the patch
20. With the patch 20 partially extended beyond the catheter 80 and
partially expanded, as shown in FIG. 4, the patch location can be
visualized angiographically relative to the aneurysm 40 and the
patch can be aligned with the aneurysm 40 before the stent is
released for the fingers 92. Pusher ring 94 prevents the stent from
moving relative to the aneurysm as the microcatheter tube 80 is
pulled back to free the proximal elliptical support ring 10 by
pushing against the proximal ring. With the stent in position, all
hardware except the stent is removed.
[0039] In another embodiment, the patch is guided into place by the
guidewire, rather than using the fingers on the pusher. In this
embodiment, the guidewire is threaded through the pusher tube and
through the proximal support ring and through a hole in the center
of the patch. The guidewire would be internal to the support ring
on the proximal end and external to the patch and support ring
distal to the center of the patch. The flexible thin patch will
allow the guidewire to lie straight in the catheter with the patch
deforming to accommodate the straight guidewire. A sandwich
polytetrafluoroethylene patch would reduce friction allowing the
guidewire to be advanced freely. The tip of the guidewire would be
advanced into the aneurysm prior to pushing the stent from the
catheter. The guidewire will tend to align the patch over the neck
of the aneurysm. Guidewire alignment may be used in conjunction
with the locked pusher/stent and radiopaque markers to aid manual
alignment or may be used in place of manual stent rotation to
automatically rotate and guide the patch into position. The
guidewire alignment may be particularly useful for locating a patch
stent at a bifurcation. The stent could be delivered with only one
end anchored in one side of the bifurcation. With one end anchored
and the guidewire in the aneurysm helping to hold the patch in
place, a second wire with an appropriate distal bend would be used
to nudge the free end of the stent into the other side of the
bifurcation.
[0040] In the above embodiments, the patch is rolled around the
central pusher tube, which pusher tube is 0.028 inches in diameter,
and the catheter tube 80 is 4 French, or about 0.052 inches in
diameter. To reach distal aneurysms, a smaller catheter will be
needed. A 2 French microcatheter and a 0.014 inch pusher tube can
be used to obtain additional flexibility for reaching more distal
aneurysms but the volume between the pusher tube and the catheter
tube is insufficient to accommodate simply rolling the patch around
the pusher tube. Therefore, an additional embodiment accommodates
smaller diameters by patterning the patch so that it may be
stretched in addition to being rolled around the pusher tube,
thereby providing a greater volume to store the stent in while it
is in the catheter. However, a stretched stent may not readily be
deployed by simply pushing the elongated stent from the catheter,
because pushing a stretched stent will tend to make it bunch up in
the catheter. Therefore, in this alternate embodiment, the stent
may need to be pulled from the catheter. To pull the stent from the
catheter tube, a forked guidewire with forks on the distal end may
be used. The forks on the guidewire are slanted towards the distal
end of the catheter, so that the fork can engage the stent
selectively, i.e., engage on a push of the forked guidewire towards
the distal end of the catheter and not engage on a pull of the
forked guidewire towards the proximal end of the catheter. The
non-forked guidewire 100 in FIG. 4 preferably will be used to
initially guide the catheter with the patch stent into place. Once
in place, the non-forked guidewire is pulled proximally from the
catheter, and the forked guidewire inserted into the catheter. As
the distal forked tip of the forked guidewire emerges from the
pusher tube, the fork springs apart and catches in the struts of
the stent. Advancing the forked guidewire will tend to pull the
stent from the catheter tube. To deploy the stent, pushing and
pulling of the forked guidewire will both be used. As the fork
nears the end of the catheter, as determined by a gauge on the
proximal end of the catheter, the forked guidewire is pulled back
to get a new bite on the stent. Advancing the forked guidewire
again will tend to pull the stent from the catheter tube further.
The forked guidewire is thus pushed and pulled until the stent is
fully deployed. When the patch is partially deployed and therefore
visible radiographically, the forked guidewire may be used to
rotate the patch into position. In this embodiment, it may be
preferable to eliminate the fingers on the pusher tube, to avoid
the need to coordinate the actions of the fingers and forks on the
stent as it is deployed.
[0041] Minor variations on the delivery method will allow the stent
to be used to treat aneurysms at bifurcations. To treat an aneurysm
at a bifurcation, the distal elliptical ring will be deployed into
one arm of the bifurcation and, after the stent patch is aligned
with the neck of the aneurysm, the second ring could be nudged into
the second arm of the bifurcation with a special pusher guidewire
bent at the distal tip and designed to catch on the support
ring.
[0042] As noted in the Brief Summary of the Invention, many
variations of the preferred embodiments are possible. The stent may
be formed from cylindrical stock instead of sheet stock to provide
more pattern options. The high percent solid area of the patch may
be obtained by using a plastic or gold disk with appropriate
fenestrations. Radiopacity may be obtained through the use of a
biodegradable or dissolvable material like iodine or iodixanol.
Superelastic tubes may be nitinol or other alloys. Nitinol may be
wrought or vacuum deposited. Heat treat parameters will be a
function of the nitinol alloy. Stent, catheter and associated
hardware sizes will be adjusted to be appropriate for the arteries
where the stents are to be used. The stent pattern and the patch
pattern may be varied extensively.
* * * * *